<!DOCTYPE html>
<html lang="en-us">
  <head>

    <meta http-equiv="content-type" content="text/html; charset=utf-8">
    
<meta charset="UTF-8">
<title>prefix 前缀查询 | Elasticsearch: 权威指南 | Elastic</title>
<link rel="home" href="index.html" title="Elasticsearch: 权威指南">
<link rel="up" href="partial-matching.html" title="部分匹配">
<link rel="prev" href="_postcodes_and_structured_data.html" title="邮编与结构化数据">
<link rel="next" href="_wildcard_and_regexp_queries.html" title="通配符与正则表达式查询">
<meta name="DC.type" content="Learn/Docs/Elasticsearch/Definitive Guide">
<meta name="DC.subject" content="Elasticsearch">
<meta name="DC.identifier" content="2.x">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <script src="https://cdn.optimizely.com/js/18132920325.js"></script>
    <link rel="apple-touch-icon" sizes="57x57" href="/apple-icon-57x57.png">
    <link rel="apple-touch-icon" sizes="60x60" href="/apple-icon-60x60.png">
    <link rel="apple-touch-icon" sizes="72x72" href="/apple-icon-72x72.png">
    <link rel="apple-touch-icon" sizes="76x76" href="/apple-icon-76x76.png">
    <link rel="apple-touch-icon" sizes="114x114" href="/apple-icon-114x114.png">
    <link rel="apple-touch-icon" sizes="120x120" href="/apple-icon-120x120.png">
    <link rel="apple-touch-icon" sizes="144x144" href="/apple-icon-144x144.png">
    <link rel="apple-touch-icon" sizes="152x152" href="/apple-icon-152x152.png">
    <link rel="apple-touch-icon" sizes="180x180" href="/apple-icon-180x180.png">
    <link rel="icon" type="image/png" href="/favicon-32x32.png" sizes="32x32">
    <link rel="icon" type="image/png" href="/android-chrome-192x192.png" sizes="192x192">
    <link rel="icon" type="image/png" href="/favicon-96x96.png" sizes="96x96">
    <link rel="icon" type="image/png" href="/favicon-16x16.png" sizes="16x16">
    <link rel="manifest" href="/manifest.json">
    <meta name="apple-mobile-web-app-title" content="Elastic">
    <meta name="application-name" content="Elastic">
    <meta name="msapplication-TileColor" content="#ffffff">
    <meta name="msapplication-TileImage" content="/mstile-144x144.png">
    <meta name="theme-color" content="#ffffff">
    <meta name="naver-site-verification" content="936882c1853b701b3cef3721758d80535413dbfd">
    <meta name="yandex-verification" content="d8a47e95d0972434">
    <meta name="localized" content="true">
    <meta name="st:robots" content="follow,index">
    <meta property="og:image" content="https://www.elastic.co/static/images/elastic-logo-200.png">
    <link rel="shortcut icon" href="/favicon.ico" type="image/x-icon">
    <link rel="icon" href="/favicon.ico" type="image/x-icon">
    <link rel="apple-touch-icon-precomposed" sizes="64x64" href="/favicon_64x64_16bit.png">
    <link rel="apple-touch-icon-precomposed" sizes="32x32" href="/favicon_32x32.png">
    <link rel="apple-touch-icon-precomposed" sizes="16x16" href="/favicon_16x16.png">
    <!-- Give IE8 a fighting chance -->
    <!--[if lt IE 9]>
    <script src="https://oss.maxcdn.com/html5shiv/3.7.2/html5shiv.min.js"></script>
    <script src="https://oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
    <![endif]-->
    <link rel="stylesheet" type="text/css" href="/guide/static/styles.css">
  </head>

  <!--© 2015-2021 Elasticsearch B.V. Copying, publishing and/or distributing without written permission is strictly prohibited.-->

  <body>
    <!-- Google Tag Manager -->
    <script>dataLayer = [];</script><noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-58RLH5" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
    <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start': new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0], j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src= '//www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f); })(window,document,'script','dataLayer','GTM-58RLH5');</script>
    <!-- End Google Tag Manager -->

    <!-- Global site tag (gtag.js) - Google Analytics -->
    <script async src="https://www.googletagmanager.com/gtag/js?id=UA-12395217-16"></script>
    <script>
      window.dataLayer = window.dataLayer || [];
      function gtag(){dataLayer.push(arguments);}
      gtag('js', new Date());
      gtag('config', 'UA-12395217-16');
    </script>

    <!--BEGIN QUALTRICS WEBSITE FEEDBACK SNIPPET-->
    <script type="text/javascript">
      (function(){var g=function(e,h,f,g){
      this.get=function(a){for(var a=a+"=",c=document.cookie.split(";"),b=0,e=c.length;b<e;b++){for(var d=c[b];" "==d.charAt(0);)d=d.substring(1,d.length);if(0==d.indexOf(a))return d.substring(a.length,d.length)}return null};
      this.set=function(a,c){var b="",b=new Date;b.setTime(b.getTime()+6048E5);b="; expires="+b.toGMTString();document.cookie=a+"="+c+b+"; path=/; "};
      this.check=function(){var a=this.get(f);if(a)a=a.split(":");else if(100!=e)"v"==h&&(e=Math.random()>=e/100?0:100),a=[h,e,0],this.set(f,a.join(":"));else return!0;var c=a[1];if(100==c)return!0;switch(a[0]){case "v":return!1;case "r":return c=a[2]%Math.floor(100/c),a[2]++,this.set(f,a.join(":")),!c}return!0};
      this.go=function(){if(this.check()){var a=document.createElement("script");a.type="text/javascript";a.src=g;document.body&&document.body.appendChild(a)}};
      this.start=function(){var a=this;window.addEventListener?window.addEventListener("load",function(){a.go()},!1):window.attachEvent&&window.attachEvent("onload",function(){a.go()})}};
      try{(new g(100,"r","QSI_S_ZN_emkP0oSe9Qrn7kF","https://znemkp0ose9qrn7kf-elastic.siteintercept.qualtrics.com/WRSiteInterceptEngine/?Q_ZID=ZN_emkP0oSe9Qrn7kF")).start()}catch(i){}})();
    </script><div id="ZN_emkP0oSe9Qrn7kF"><!--DO NOT REMOVE-CONTENTS PLACED HERE--></div>
    <!--END WEBSITE FEEDBACK SNIPPET-->

    <div id="elastic-nav" style="display:none;"></div>
    <script src="https://www.elastic.co/elastic-nav.js"></script>

    <!-- Subnav -->
    <div>
      <div>
        <div class="tertiary-nav d-none d-md-block">
          <div class="container">
            <div class="p-t-b-15 d-flex justify-content-between nav-container">
              <div class="breadcrum-wrapper"><span><a href="/guide/" style="font-size: 14px; font-weight: 600; color: #000;">Docs</a></span></div>
            </div>
          </div>
        </div>
      </div>
    </div>

    <div class="main-container">
      <section id="content">
        <div class="content-wrapper">

          <section id="guide" lang="zh_cn">
            <div class="container">
              <div class="row">
                <div class="col-xs-12 col-sm-8 col-md-8 guide-section">
                  <!-- start body -->
                  <div class="page_header">
<b>请注意:</b><br>本书基于 Elasticsearch 2.x 版本，有些内容可能已经过时。
</div>
<div id="content">
<div class="breadcrumbs">
<span class="breadcrumb-link"><a href="index.html">Elasticsearch: 权威指南</a></span>
»
<span class="breadcrumb-link"><a href="search-in-depth.html">深入搜索</a></span>
»
<span class="breadcrumb-link"><a href="partial-matching.html">部分匹配</a></span>
»
<span class="breadcrumb-node">prefix 前缀查询</span>
</div>
<div class="navheader">
<span class="prev">
<a href="_postcodes_and_structured_data.html">« 邮编与结构化数据</a>
</span>
<span class="next">
<a href="_wildcard_and_regexp_queries.html">通配符与正则表达式查询 »</a>
</span>
</div>
<div class="section">
<div class="titlepage"><div><div>
<h2 class="title">
<a id="prefix-query"></a>prefix 前缀查询<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elasticsearch-cn/elasticsearch-definitive-guide/edit/cn/130_Partial_Matching/10_Prefix_query.asciidoc">edit</a>
</h2>
</div></div></div>
<p>为了找到所有以 <code class="literal">W1</code> 开始的邮编，可以使用简单的 <code class="literal">prefix</code> 查询：</p>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">GET /my_index/address/_search
{
    "query": {
        "prefix": {
            "postcode": "W1"
        }
    }
}</pre>
</div>
<div class="sense_widget" data-snippet="snippets/130_Partial_Matching/10_Prefix_query.json"></div>
<p><code class="literal">prefix</code> 查询是一个词级别的底层的查询，它不会在搜索之前分析查询字符串，它假定传入前缀就正是要查找的前缀。</p>
<div class="tip admon">
<div class="icon"></div>
<div class="admon_content">
<p>默认状态下， <code class="literal">prefix</code> 查询不做相关度评分计算，它只是将所有匹配的文档返回，并为每条结果赋予评分值 <code class="literal">1</code> 。它的行为更像是过滤器而不是查询。 <code class="literal">prefix</code> 查询和 <code class="literal">prefix</code> 过滤器这两者实际的区别就是过滤器是可以被缓存的，而查询不行。</p>
</div>
</div>
<p>之前已经提过：“只能在倒排索引中找到存在的词”，但我们并没有对这些邮编的索引进行特殊处理，每个邮编还是以它们精确值的方式存在于每个文档的索引中，那么 <code class="literal">prefix</code> 查询是如何工作的呢？</p>
<p class="pagebreak-after">回想倒排索引包含了一个有序的唯一词列表（本例是邮编）。对于每个词，倒排索引都会将包含词的文档 ID 列入 <em>倒排表（postings list）</em> 。与示例对应的倒排索引是：</p>
<pre class="literallayout">Term:          Doc IDs:
-------------------------
"SW5 0BE"    |  5
"W1F 7HW"    |  3
"W1V 3DG"    |  1
"W2F 8HW"    |  2
"WC1N 1LZ"   |  4
-------------------------</pre>

<p>为了支持前缀匹配，查询会做以下事情：</p>
<div class="olist orderedlist">
<ol class="orderedlist">
<li class="listitem">
扫描词列表并查找到第一个以 <code class="literal">W1</code> 开始的词。
</li>
<li class="listitem">
搜集关联的文档 ID 。
</li>
<li class="listitem">
移动到下一个词。
</li>
<li class="listitem">
如果这个词也是以 <code class="literal">W1</code> 开头，查询跳回到第二步再重复执行，直到下一个词不以 <code class="literal">W1</code> 为止。
</li>
</ol>
</div>
<p>这对于小的例子当然可以正常工作，但是如果倒排索引中有数以百万的邮编都是以 <code class="literal">W1</code> 开头时，前缀查询则需要访问每个词然后计算结果！</p>
<p>前缀越短所需访问的词越多。如果我们要以 <code class="literal">W</code> 作为前缀而不是 <code class="literal">W1</code> ，那么就可能需要做千万次的匹配。</p>
<div class="caution admon">
<div class="icon"></div>
<div class="admon_content">
<p><code class="literal">prefix</code> 查询或过滤对于一些特定的匹配是有效的，但使用方式还是应当注意。当字段中词的集合很小时，可以放心使用，但是它的伸缩性并不好，会对我们的集群带来很多压力。可以使用较长的前缀来限制这种影响，减少需要访问的量。</p>
</div>
</div>
<p>本章后面会介绍另一个索引时的解决方案，这个方案能使前缀匹配更高效，不过在此之前，需要先看看两个相关的查询： <code class="literal">wildcard</code> 和 <code class="literal">regexp</code> （模糊和正则）。</p>
</div>
<div class="navfooter">
<span class="prev">
<a href="_postcodes_and_structured_data.html">« 邮编与结构化数据</a>
</span>
<span class="next">
<a href="_wildcard_and_regexp_queries.html">通配符与正则表达式查询 »</a>
</span>
</div>
</div>

                  <!-- end body -->
                </div>
                <div class="col-xs-12 col-sm-4 col-md-4" id="right_col">
                  <div id="rtpcontainer" style="display: block;">
                    <div class="mktg-promo">
                      <h3>Most Popular</h3>
                      <ul class="icons">
                        <li class="icon-elasticsearch-white"><a href="https://www.elastic.co/webinars/getting-started-elasticsearch?baymax=default&amp;elektra=docs&amp;storm=top-video">Get Started with Elasticsearch: Video</a></li>
                        <li class="icon-kibana-white"><a href="https://www.elastic.co/webinars/getting-started-kibana?baymax=default&amp;elektra=docs&amp;storm=top-video">Intro to Kibana: Video</a></li>
                        <li class="icon-logstash-white"><a href="https://www.elastic.co/webinars/introduction-elk-stack?baymax=default&amp;elektra=docs&amp;storm=top-video">ELK for Logs &amp; Metrics: Video</a></li>
                      </ul>
                    </div>
                  </div>
                </div>
              </div>
            </div>
          </section>

        </div>


<div id="elastic-footer"></div>
<script src="https://www.elastic.co/elastic-footer.js"></script>
<!-- Footer Section end-->

      </section>
    </div>

<script src="/guide/static/jquery.js"></script>
<script type="text/javascript" src="/guide/static/docs.js"></script>
<script type="text/javascript">
  window.initial_state = {}</script>
  </body>
</html>
